Molecular-beam-epitaxy grown InAs islands on nominal and vicinal GaAs(2Â 5Â 11)A surfaces

InAs was deposited onto nominal and vicinal (1.0°-off-oriented) GaAs(2 5 11)A surfaces by means of molecular beam epitaxy and studied by scanning tunneling microscopy and photoluminescence measurements. Both surfaces show step bunches along the [311¯] direction which form fairly large (0 1 1) nano-facets. Large, inhomogeneously distributed InAs islands are formed on these nano-facets. The InAs islands exhibit a wide size distribution and vanishing photoluminescence intensity, both being characteristic for incoherent islands. The shape of the incoherent InAs islands is composed mainly of (1 1 1)A, (0 1 1), (0 0 1), and (3 1 7)A surfaces. During growth the latter undergoes a transition into the steeper (1 0 1) facet. The shape of the incoherent islands exhibits no symmetry in accordance with the missing of any symmetry at the GaAs(2 5 11)A bulk-truncated substrate surface. On the flat terraces of the nominal GaAs(2 5 11)A surface a second kind of QDs develops which are of the same shape but of a sharp size distribution. The photoluminescence intensity of the latter is quenched presumably by the coexistent incoherent InAs islands.